Process for preparing MTT zeolites using N,N,N,N′,N′,N′-hexamethyl-propane-1,3-diammonium dication structure directing agent

ABSTRACT

The present invention rebates to a process for preparing zeolites having the MTT framework topology defined by the connectivity of the tetrahedral atoms in the zeolite, such as zeolites SSZ-32 and ZSM-23, using an N,N,N,N′,N′,N′-hexamethyl-propane-1,3-diammonium dication as a structure directing agent.

This application is a Continuation-In-Part of application Ser. No.11/216,546, filed Aug. 30, 2005 now U.S. Pat. No. 7,157,075.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing zeolites havingthe MTT framework topology defined by the connectivity of thetetrahedral atoms in the zeolite using the following structure directingagent:

-   -   N,N,N,N′N′N′-Hexamethyl-propane-1,3-diammonium cation.

2. State of the Art

Zeolites having the MTT framework topology defined by the connectivityof the tetrahedral atoms (referred to herein simply as MTT) are known.See, for example, Ch. Baerlocher et al., Atlas of Zeolite FrameworkTypes, 5^(th) Revised Edition, 2001 of the International ZeoliteAssociation. Examples of MTT zeolites include the zeolite designated“SSZ-32”. SSZ-32 and methods for making it are disclosed in U.S. Pat.No. 5,053,373, issued Oct. 1, 1991 to Zones. This patent discloses thepreparation of zeolite SSZ-32 using in N-loweralkyl-N′-isopropylimidazolium cation as an organic structure directingagent (SDA), sometimes called a templating agent. U.S. Pat. No.4,076,842, issued Feb. 28, 1978 to Plank et al., discloses thepreparation of the zeolite designated “ZSM-23”, a zeolite with astructure similar to SSZ-32, using a cation derived from pyrrolidine asthe SDA. Zeolites SSZ-32 and ZSM-23 are commonly referred to as havingthe MTT framework topology. Both of the aforementioned patents areincorporated herein by reference in their entirety. Other MTT zeolitesinclude EU-13, ISI-4 and KZ-1.

U.S. Pat. No. 5,707,600, issued Jan. 13, 1998 to Nakagawa et al.,discloses a process for preparing medium pore size zeolites, includingSSZ-32, using small, neutral amines. The amines contain (a) only carbon,nitrogen and hydrogen atoms, (b) one primary, secondary or tertiary, butnot quaternary, amino group, and (c) a tertiary nitrogen atom, at leastone tertiary carbon atom, or a nitrogen atom bonded directly to at leastone secondary carbon atom, wherein the process is conducted in theabsence of a quaternary ammonium compound. Examples of the small aminesinclude isobutylamine, diisobutylamine, trimethylamine,cyclopentylamine, diisopropylamine, sec-butylamine,2,5-dimethylpyrrolidine and 2,6-dimethylpiperidine.

U.S. Pat. No. 5,707,601 issued Jan. 13, 1998 to Nakagawa, discloses aprocess for preparing MTT zeolites using small, neutral amines. Theamines contain (a) only carbon, nitrogen and hydrogen atoms, (b) oneprimary, secondary, or tertiary, but not quaternary, amino group, and(c) a tertiary nitrogen atom, at least one tertiary carbon atom, or anitrogen atom bonded directly to at least one secondary carbon atom,wherein the process is conducted in the absence of a quaternary ammoniumcompound. Examples of the small amines include isobutylamine,diisobutylamine, trimethylamine, cyclopentylamine, diisopropylamine,sec-butylamine, 2,5-dimethylpyrrolidine and 2,6-dimethylpiperidine.

U.S. Pat. No. 5,785,947, issued Jul. 28, 1998 to Zones et al., disclosesthat zeolites, including medium pore size, unidimensional zeolites, canbe prepared using a mixture of an amine component comprising (1) atleast one amine containing one to eight carbon atoms, ammoniumhydroxide, and mixtures thereof, and (2) an organic templating compoundcapable of forming the zeolite in the presence of the amine component,wherein the amine is smaller than the organic templating compound.Examples of the amines include isopropylamine, isobutylamine,n-butylamine, piperidine, 4-methylpiperidine, cyclohexylamine,1,1,3,3-tetramethylbutylamine and cyclopentylamine and mixtures of suchamines.

U.S. Pat. No. 5,332,566, issued Jul. 26, 1994 to Moini, discloses amethod of synthesizing ZSM-23 (i.e., MTT) using an organic directingagent having the structure:

U.S. Pat. No. 6,475,464, issued Nov. 5, 2002 to Rouleau et al.,discloses the preparation of MTT zeolites using alkylated polymethyleneα-ω diammonium derivatives acting as a template or structure directingagent. These derivatives are defined by the formulaR₁R₂R₃N⁺(CH₂)_(n)N⁺R₄R₅R₆, n being in the range 3 to 14 and R₁ to R₆,which may be identical or different, representing alkyl or hydroxylalkylradicals containing 1 to 8 carbon atoms; up to five R₁ to R₆ radicalscan be hydrogen. N,N,N,N′,N′N′-hexamethyl-propane-1,3-diammoniumdication is not specifically disclosed, nor is it used in any of theexamples. It is disclosed that the MTT zeolite may be prepared usingalkali metal or ammonium ion. Sodium or ammonium cations are used in theexamples. It is also required that the reaction mixture contain seedcrystals of a zeolite other than a MTT zeolite.

It has now been found that MTT zeolites, such as SSZ-32, can be preparedusing structure directing agentN,N,N,N′,N′N′-hexamethyl-propane-1,3-diammonium dication.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a processfor preparing, MTT zeolites, said process comprising:

-   -   (a) preparing a reaction mixture comprising (1) sources of        potassium oxide; (2) optionally, sources of an oxide selected        from the oxides of aluminum, boron, iron, gallium, titanium,        vanadium or mixtures thereof; (3) sources of silicon oxide; (4)        a structure directing agent comprising a        N,N,N,N′,N′N′-hexamethyl-propane-1,3-diammonium dication        (hereinafter also referred to as “SDA Q”) and (5) water;    -   (b) maintaining the reaction mixture under conditions sufficient        to form crystals of the zeolite; and    -   (c) recovering the crystals of the zeolite.

In one embodiment, the present invention provides said process which isperformed in the absence of any nitrogen-containing organic compoundother than SDA Q. In another embodiment, the process is conducted in theabsence of seed crystals of a zeolite different from MTT zeolite.

The present invention also provides MTT zeolites whose composition,as-synthesized and in the anhydrous state, in terms of mole ratios, isas follows:

YO₂/W_(c)O_(d)   15-∞ Q/YO₂  0.02-0.10 K/YO₂ 0.005-0.10wherein Y is silicon; W is aluminum, boron, gallium, indium, iron,titanium, vanadium or mixtures thereof; c is 1 or 2; d is 2 when c is 1(i.e., W is tetravalent) or d is 3 or 5 when c is 2 (i.e., d is 3 when Wis trivalent or 5 when W is pentavalent); and Q is

-   -   N,N,N,N′N′N′-Hexamethyl-propane-1,3-diammonium cation.

The present invention also provides a preferred embodiment of thiscomposition wherein said composition does not contain anynitrogen-containing organic templating agent other than SDA Q.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention comprises:

-   -   (a) preparing a reaction mixture comprising (1) sources of        potassium oxide; (2) optionally, sources of an oxide selected        from the oxides of aluminum, iron, boron, gallium, indium,        titanium, vanadium or mixtures thereof; (3) sources of silicon        oxide: (4) the following structure directing agent:

-   -   -   N,N,N,N′N′N′-Hexamethyl-propane-1,3-diammonium cation            and (5) water;

    -   (b) maintaining the reaction mixture under conditions sufficient        to form crystals of the zeolite; and

    -   (c) recovering the crystals of the zeolite.

The process of the present invention comprises forming a reactionmixture from sources of potassium cations; optionally, sources of anoxide of aluminum, boron, iron, gallium, indium, titanium, vanadium ormixtures thereof (W); sources of an oxide of silicon oxide (Y); SDA Q(Q); and water, said reaction mixture having a composition in terms ofmole ratios within the following ranges:

TABLE A Reactants General Preferred YO₂/W_(a)O_(b) 15-∞ 30-80 OH⁻/YO₂0.10-0.50 0.15-0.30 Q/YO₂ 0.05-0.50 0.10-0.40 K/YO₂ 0.05-0.500.075-0.30  H₂O/YO₂ 10-70 25-50where Y is silicon; W is aluminum, boron, gallium, indium, iron,titanium, vanadium; a is 1 or 2, b is 2 when a is 1 (i.e., W istetravalent); b is 3 when a is 2 (i.e., W is trivalent); and Q is SDA Q.

Embodiments of the process of this invention include reaction mixturesin which the YO₂/W_(a)O_(b) mole ratio is from about 20 to about 80;from about 20 to less than 40; 40 or more; and from 40 to about 80.

Typical sources of aluminum oxide for the reaction mixture includealuminates, alumina, hydrated aluminum hydroxides, and aluminumcompounds such as AlCl₃ and Al₂(SO₄)₃. Typical sources of silicon oxideinclude silica hydrogel, silicic acid, colloidal silica, tetraalkylorthosilicates, silica hydroxides, and fumed silicas. Other metals canbe added in forms corresponding to their aluminum and siliconcounterparts. Trivalent elements stabilized on silica colloids are alsouseful reagents.

The SDA useful in the process of the present invention is SDA Q havingthe following formula:

-   -   N,N,N,N′N′N′-Hexamethyl-propane-1,3-diammonium cation

In preparing MTT zeolites in accordance with the present invention, thereactants and SDA Q can be dissolved in water and the resulting reactionmixture maintained at an elevated temperature until crystals are formed.The reaction is conducted at about 150° C. It has been found that thistemperature achieves good results. The crystallization period istypically 6-21 days, and generally about 7-14 days.

The hydrothermal crystallization is usually conducted under pressure andusually in an autoclave so that the reaction mixture is subject toautogenous pressure. The reaction mixture should be stirred duringcrystallization.

Once the crystals have formed, the solid product is separated from thereaction mixture by standard mechanical separation techniques, such asfiltration. The crystals are water-washed and then dried, e.g., at 90°C. to 150° C. for from 8 to 24 hours, to obtain the as-synthesizedzeolite crystals. The drying step can be performed at atmospheric orsubatmospheric pressures.

During the hydrothermal crystallization step, the crystals can beallowed to nucleate spontaneously from the reaction mixture. Thereaction mixture can also be seeded with crystals of the desired MTTzeolite both to direct, and accelerate the crystallization, as well asto minimize the formation of any undesired crystalline phases. When seedcrystals are used, typically about 0.5% to about 5.0% (based on theweight of silica used in the reaction mixture) of the seed crystals ofthe desired zeolite are added. It is not necessary to use crystals of azeolite other than MTT zeolite. In one embodiment, the MTT zeolite isformed in the presence of potassium and SDA Q, but in the absence ofseed crystals of a zeolite different from MTT zeolite.

Due to the unpredictability of the factors which control nucleation andcrystallization in the art of crystalline oxide synthesis, not everycombination of reagents, reactant ratios, and reaction conditions willresult in crystalline products. Selecting crystallization conditionswhich are effective for producing crystals may require routinemodifications to the reaction mixture or to the reaction conditions,such as temperature, and/or crystallization time. Making thesemodifications are well within the capabilities of one skilled in theart.

The as-synthesized MTT zeolite product made by the process of thisinvention has an as-synthesized composition comprising, in terms of moleratios in the anhydrous state, the following:

YO₂/W_(c)O_(d)   15-∞ Q/YO₂  0.02-0.10 K/YO₂ 0.005-0.10wherein Y is silicon; W is aluminum, boron, gallium, indium, iron,titanium, vanadium or mixtures thereof; c is 1 or 2; d is 2 when c is 1or d is 3 or 5 when c is 2; Q is SDA Q. In one embodiment, Y is siliconand W is aluminum. The YO₂/W_(c)O_(d) ratio may be from about 20 toabout 80. In one embodiment of this invention, the YO₂/W_(c)O_(d) ratiois from about 20 to less than 40, and in another embodiment this ratiois greater than 40, e.g., from 40 to about 80.

The MTT zeolites can be made with a mole ratio of YO₂/W_(c)O_(d) of ∞,i.e., there is essentially no W_(c)O_(d) present in the MTT zeolite. Inthis case, the zeolite would be an all-silica material. Thus, in atypical case where oxides of silicon and aluminum are used, the MTTzeolite can be made essentially aluminum free, i.e., having a silica toalumina mole ratio of ∞. One method of increasing the mole ratio ofsilica to alumina is by using standard acid leaching or chelatingtreatments. However, essentially aluminum-free MTT zeolites can besynthesized using essentially aluminum-free silicon sources as the maintetrahedral metal oxide component. The MTT zeolites can also be prepareddirectly as an aluminosilicate.

Lower silica to alumina ratios may also be obtained by using methodswhich insert aluminum into the crystalline framework. For example,aluminum insertion may occur by thermal treatment of the zeolite incombination with an alumina binder or dissolved source of alumina. Suchprocedures are described in U.S. Pat. No. 4,559,315, issued on Dec. 17,1985 to Chang et al.

Typically, the zeolite is thermally treated (calcined) prior to use as acatalyst.

Usually, it is desirable to remove the potassium cation by ion exchangeand replace it with hydrogen, ammonium, or any desired metal ion. Thezeolite can be leached with chelating agents, e.g., EDTA or dilute acidsolutions, to increase the silica/alumina mole ratio. The zeolite canalso be steamed; steaming helps stabilize the crystalline lattice toattack from acids. The zeolite can be used in intimate combination withhydrogenating components, such as tungsten, vanadium molybdenum,rhenium, nickel cobalt, chromium, manganese, or a noble metal, such aspalladium or platinum, for those applications in which ahydrogenation-dehydrogenation function is desired. Typical replacingcations can include hydrogen and hydrogen precursors, rare earth metals,and metals from Groups IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VIB, and VIIIof the Periodic Table of Elements. Of the replacing cations, hydrogenand cations of metals such as rare earth, Mn, Ca, Mg, Zn, Cd, Pt, Pd,Ni, Co, Ti, Al, Sn, Ga, In and Fe are particularly preferred.

The X-ray diffraction pattern of Table I is representative of a calcinedMTT zeolite (in this case SSZ-32) made in accordance with thisinvention. Minor variations in the diffraction pattern can result fromvariations in the silica-to-alumina mole ratio of the particular sampledue to changes in lattice constants. In addition, sufficiently smallcrystals will affect the shape and intensity of peaks, leading tosignificant peak broadening. The variation in the scattering angle (twotheta) measurements, due to instrument error and to differences betweenindividual samples, is estimated at +/−0.10 degrees.

The X-ray powder diffraction pattern was determined by standardtechniques. The radiation was the K-alpha/doublet of copper. Adiffractometer with a scintillation counter detector was used. The peakheights I and the positions, as a function of 2Theta where Theta is theBragg angle, were read from the relative intensities, 100×I/I_(o) whereI_(o) is the intensity of the strongest line or peak, and d, theinterplanar spacing in Angstroms corresponding to the recorded lines,can be calculated.

TABLE I CALCINED MTT ZEOLITE 2Theta d Rel I^(a) 7.90^(b) 11.18 VS8.12^(b) 10.88 VS 8.86 9.97 M 11.38 7.76 S 14.60 6.06 W 15.86 5.58 W16.32 5.43 W 18.12 4.89 W 19.72 4.50 VS 20.96 4.24 VS 22.86 3.89 VS24.02 3.70 VS 24.62 3.61 S-VS 25.28 3.52 M 25.98 3.43 S 28.26 3.16 W31.60 2.83 W 35.52 2.52 S ^(a)The X-ray patterns provided are based on arelative intensity scale in which the strongest line in the X-raypattern is assigned a value of 100: W(weak) is less than 20; M(medium)is between 20 and 40: S(strong) is between 40 and 60; VS(very strong) isgreater than 60. ^(b)These two peaks may have significant overlap, andare sometimes treated as a single peak.

Table IA below shows an X-ray diffraction pattern representative of acalcined MTT zeolite (SSZ-32) made in accordance with this invention. InTable IA, the intensity (I) of the peaks or lines is expressed as theintensity relative to the strongest peak or line in the pattern, i.e.,I/I_(o)×100 where I_(o) is the intensity of the strongest peak or line.

TABLE IA CALCINED MTT ZEOLITE 2Theta d I/I_(o) × 100 7.90^(b) 11.18 71.88.12^(b) 10.88 86.1 8.86 9.97 32.6 11.38 7.76 49.3 14.60 6.06 6.4 15.865.58 11.4 16.32 5.43 14.6 18.12 4.89 10.2 19.72 4.50 100.0 20.96 4.2473.9 22.86 3.89 92.1 24.02 3.70 92.1 24.62 3.61 65.4 25.28 3.52 35.725.98 3.43 46.0 28.26 3.16 13.3 31.60 2.83 16.2 35.52 2.52 50.4^(b)These two peaks may have significant overlap, and are sometimestreated as a single peak.

The X-ray diffraction pattern of Table II shows the major peaks of anas-synthesized MTT zeolite (in this case SSZ-32), in the anhydrousstate, made in accordance with this invention.

TABLE II AS-SYNTHESIZED MTT ZEOLITE 2Theta d Rel I 8.19^(c) 10.79 S 8.959.87 M 11.42 7.74 M 16.41 5.40 W 18.20 4.87 W 19.76 4.49 VS 21.01 4.22VS 22.94 3.87 VS 24.09 3.69 VS 24.70 3.60 S 26.05 3.42 S 35.57 2.52 S^(c)Quite likely two peaks overlapped.

Table IIA below shows the major peaks of a typical X-ray diffractionpattern for as-synthesized MTT zeolite made in accordance with thisinvention, including the relative intensities of the peaks or lines.

TABLE IIA AS-SYNTHESIZED MTT ZEOLITE 2Theta d I/I_(o) × 100 8.19^(c)10.79 56.3 8.95 9.87 23.9 11.42 7.74 35.4 16.41 5.40 9.5 18.20 4.87 13.019.76 4.49 100.0 21.01 4.22 85.6 22.94 3.87 95.7 24.09 3.69 80.3 24.703.60 60.9 26.05 3.42 49.9 35.57 2.52 48.9 ^(c)Quite likely two peaksoverlapped.

Calcination can also result in changes in the intensities of the peaksas well as minor shifts in the diffraction pattern. The zeolite producedby exchanging the metal or other cations present in the zeolite withvarious other cations (such as H⁺ or NH₄ ⁺) yields essentially the samediffraction pattern, although again, there may be minor shifts in theinterplanar spacing and variations in the relative intensities of thepeaks. Notwithstanding these minor perturbations, the basic crystallattice remains unchanged by these treatments.

The MTT zeolites prepared by the process of this invention are useful inhydrocarbon conversion reactions. Hydrocarbon conversion reactions arechemical and catalytic processes in which carbon-containing compoundsare changed to different carbon-containing compounds. Examples ofhydrocarbon conversion reactions include catalytic cracking,hydrocracking, dewaxing, alkylation, isomerization, olefin and aromaticsformation reactions, and aromatics isomerization and disproportionation.

The following examples demonstrate, but do not limit, the presentinvention.

EXAMPLES

There are numerous variations on the embodiments of the presentinvention which are possible in light of the teachings supporting thepresent invention. Reheis F-2000) alumina (53-56 wt %. Al₂O₃ availablefrom Reheis Chemical Co.) was used as the aluminum source and KOH wasused as the potassium source. Cabosil M-5 fused silica was used as thesilica source. The reaction was performed within a Blue-M convectionoven on a spit rotating at 43 rpm.

The synthesis was performed as follows: 3.75 g 1N KOH aqueous solution,0.62 g SDA Q in the iodide form, and 9.1 g deionized H₂O were mixedtogether in a 23 mL Teflon cup. Next, 0.044 g Reheis F-2000 was addedand mixed thoroughly to yield a uniform mixture. Finally, 0.90 g CabosilM-5 was added, and the resultant gel was thoroughly homogenized bymixing with a spatula by hand. The reaction mixture had the mole ratiosshown in the table below. The Teflon reactor was then capped and sealedinside a Parr autoclave. The autoclave was then placed in an oven with arotating spit (43 rpm) and heated at 150° C. for 24 days. After thereaction was completed, the reaction mixture was removed, cooled to roomtemperature, and then the reactor contents were filtered under vacuum ina glass filtration funnel, and the crystals that formed were recoveredusing standard techniques. The resulting crystals were MTT zeolite.

Time Temp. KOH/ SDA (days) C. SiO2^(a) SDA Q/SiO2^(a) SAR^(b) Phase SDAQ 28 150 0.25 0.20 SAR = 66 MTT ^(a)Mole ratios ^(b)SAR = silica/aluminamole ratio

1. A process for preparing a zeolite having the MTT framework topologydefined by the connectivity of the tetrahedral atoms in the zeolite,said process comprising: (a) preparing a reaction mixture comprising (1)sources of potassium oxide; (2) optionally, sources of an oxide selectedfrom the oxides of aluminum, boron, iron, gallium, titanium, vanadium ormixtures thereof (3) sources of silicon oxide; (4) a structure directingagent comprising a N,N,N,N′,N′N′-hexamethyl-propane-1,3-diammoniumdication (hereinafter also referred to as “SDA Q”) and (5) water; (b)maintaining the reaction mixture under conditions sufficient to formcrystals of the zeolite; and (c) recovering the crystals of the zeolite.2. The process of claim 1 wherein said reaction mixture comprises, interms of mole ratios, the following: YO₂/W_(a)O_(b) 15~∞ OH⁻/YO₂0.10-0.50 Q/YO₂ 0.05-0.50 K/YO₂ 0.05-0.50 H₂O/YO₂ 10-70

where Y is silicon; W is aluminum, boron, gallium, indium, iron,titanium, vanadium; a is 1 or 2, b is 2 when a is 1; b is 3 when a is 2;and Q is

N,N,N,N′N′N′-Hexamethyl-propane-1,3-diammonium cation.
 3. The process ofclaim 2 wherein said aqueous solution comprises, in terms of moleratios, the following: YO₂/W_(a)O_(b) 30-80 OH⁻/YO₂ 0.15-0.30 Q/YO₂0.10-0.40 M_(2/n)/YO₂ 0.075-0.30  H₂O/YO₂  25-50.


4. The process of claim 2 wherein Y is silicon and W is aluminum.
 5. Theprocess of claim 2 wherein the YO₂/W_(a)O_(b) mole ratio is from about20 to about
 80. 6. The process of claim 2 wherein the YO₂/W_(a)O_(b)mole ratio is from about 20 to less than
 40. 7. The process of claim 2wherein the YO₂/W_(a)O_(b) mole ratio is 40 or more.
 8. The process ofclaim 2 wherein the YO₂/W_(a)O_(b) mole ratio is from about 40 to about80.
 9. The process of claim 1 further comprising replacing the potassiumcations of the recovered zeolite, at least in part, by ion exchange witha cation or mixture of cations selected from the group consisting ofhydrogen and hydrogen precursors, rare earth metals, and metals fromGroups IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VIB, and VIII of the PeriodicTable of Elements.
 10. The process of claim 9 wherein said replacingcation is hydrogen or a hydrogen precursor.
 11. A zeolite having the MTTframework topology defined by the connectivity of the tetrahedral atomsin the zeolite and having a composition, as-synthesized and in theanhydrous state, in terms of mole ratios, as follows: YO₂/W_(c)O_(d)  15~∞ Q/YO₂  0.02-0.10 K/YO₂ 0.005-0.10

wherein Y is silicon; W is aluminum, boron, gallium, indium, irontitanium, vanadium or mixtures thereof; c is 1 or 2; d is 2 when c is 1or d is 3 or 5 when c is 2; and Q is

N, N, N,N′N′N′-Hexamethyl-propane-1,3-diammonium cation.
 12. The zeoliteof claim 11 wherein Y is silicon and W is aluminum.
 13. The zeolite ofclaim 11 wherein the YO₂/W_(c)O_(d) mole ratio is from about 20 to about80.
 14. The zeolite of claim 11 wherein the YO₂/W_(c)O_(d) mole ratio isfrom about 20 to less than
 40. 15. The zeolite of claim 11 wherein theYO₂/W_(c)O_(d) mole ratio is 40 or more.
 16. The zeolite of claim 11wherein the YO₂/W_(c)O_(d) mole ratio is from about 40 to about 80.